What are the three main gases in the air and their approximate percentages?

The three main gases in Earth's atmosphere are indeed oxygen, nitrogen, and carbon dioxide. Understanding their approximate percentages is crucial for divers, as these gases play significant roles in respiratory functions and the management of gas mixtures during diving activities.

Oxygen makes up about 20% of the atmosphere, which is vital for respiration and is the gas we strive to maintain at optimal levels while underwater. Nitrogen, which constitutes approximately 79% of the air we breathe, is inert and does not support respiration, but it does dissolve in the blood and tissues and is a significant factor in the formation of nitrogen narcosis or decompression sickness during dives. Carbon dioxide is present in trace amounts, around 0.03%, and is a waste product of respiration that the body must expel to maintain proper acid-base balance.

The other options contain inaccuracies in their values of these gases, making them less accurate representations of the atmospheric composition. The correct answer provides a clear and accurate view of the air's composition, which is essential for both general knowledge and safe diving practices.